strange socket behaviour

[Joe Wong]

Hello,

I have a short program that the client make a connection to server, a thread is then created to poll any data sent from the server. The main thread will close the socket after 5 seconds. Here are the code:

from socket import *
import select
import threading
import time

def poll(c):
i, o, e = select.select([c], [], [])
if not i:
print "time out"
return
print i
data = i[0].recv(1024)
print "data: ", data

if __name__=="__main__":
c = socket(AF_INET, SOCK_STREAM)
c.connect(('192.168.100.74', 8888))
th=threading.Thread(None, poll, "", (c, ))
th.setDaemon(1)
th.start()

time.sleep(5)
c.shutdown(2)
c.close()
th.join()
print "completed"

On Windows, as soon as client socket 'c' is closed, the select() call returns. However, on Linux, the program seems blocking forever ( may be I am not patient to wait ). Is there anything wrong with my code?

Regards,

-- Wong

 

[fishboy]

Hello,

I have a short program that the client make a connection to server, a thread is then created to poll any data sent from the server. The main thread will close the socket after 5 seconds. Here are the code:

from socket import *
import select
import threading
import time

def poll(c):
i, o, e = select.select([c], [], [])
if not i:
print "time out"
return
print i
data = i[0].recv(1024)
print "data: ", data

if __name__=="__main__":
c = socket(AF_INET, SOCK_STREAM)
c.connect(('192.168.100.74', 8888))
th=threading.Thread(None, poll, "", (c, ))
th.setDaemon(1)
th.start()

time.sleep(5)
c.shutdown(2)
c.close()
th.join()
print "completed"

On Windows, as soon as client socket 'c' is closed, the select() call returns. However, on Linux, the program seems blocking forever ( may be I am not patient to wait ). Is there anything wrong with my code?

Regards,

-- Wong

No, your code is ok. It's just that closing the local end of the
socket is undefined in select(). Which is why Windows does one thing
and Linux the other.

Closing the remote end causes the socket to show up as readable with
zero data.

 

[Chris Reay]

snip

No, your code is ok. It's just that closing the local end of the
socket is undefined in select(). Which is why Windows does one thing
and Linux the other.

Closing the remote end causes the socket to show up as readable with
zero data.

Precisely. I've been through this myself. My solution on the FreeBSD
server side is (pardon the bad pseudocode):

rd, wr, err = select(myClientSocksList, [], myClientSocksList,
myTimeOut)
for eachSock in rd:
try:
dataIn = eachSock.recv(MaxBufSz)
except socket.error:
# Server closes session.
self.closeSession(eachSock, "Socket error - recv")
else:
if len(dataIn) > 0:
# Process, process.
else:
# Server closes session.
self.closeSession(eachSock, "Recvd 0 bytes")
# Check the err list etc, etc.